Gene therapy can stop severe bleeding in dogs with hemophilia, a new study shows.

The blood clotting disorder hemophilia A affects about 1 in 10,000 men and causes them to bleed severely because of deficiencies in the blood clotting protein, Factor VIII. Researchers used a virus to insert functional human Factor VIII genes into the blood stem cells of three dogs. All three dogs stored the resulting Factor VIII proteins in their platelets, and the two dogs producing the most blood-clotting protein lived without severe bleeds for 2.5 years after therapy, the team reports November 19 in Nature Communications.

Targeting human blood cells in a similar way may control severe bleeding in people who suffer from hemophilia A, the researchers say.